The present invention is directed to transferred electron oscillators (TEOs), and more particularly to methods for fabricating InP TEOs.
Indium phosphide has excellent material properties for the operation of TEO devices in the millimeter-wave region of the radio spectrum. As a result of these material properties, high efficiency oscillators and low-noise broadband amplifiers have been developed. The devices used for the oscillator and amplifier development have been fabricated on n.sup.+ substrates, and accordingly, integration within a monolithic format is not easily achieved. For further application in millimeter-wave monolithic circuits, this work has focused on the development of a planar transferredelectron device formed on a semi-insulating substrate.
Planar InP TEOs have been constructed whose design includes a localized high resistivity region near the cathode contact. The high resistivity region, referred to as a notch, partially extends into the active layer and is formed by selective boron implanatation damage. This design creates a localized high electric field region, which produces a laterally uniform well-defined space-charge nucleation site. The notched devices demonstrate significantly superior microwave performance compared to devices without a notch. At x-band, notched TEO devices operate with direct current (DC) to radio frequency (RF) conversion efficiencies of up to 4.5 percent, while the TEO devices without a notch operate with an efficiency of less than 1 percent.
However for highest efficiency, the region of selective ion implantation must be aligned between the TEO device cathode and anode contacts, as close as possible to the cathode contact. As the device dimensions are decreased to meet the need of higher frequency operation, a different method of fabrication must be employed to accurately position the notch next to the cathode contact.